The invention relates to an arrangement for multistage vacuum and molecular distilling or evaporating liquid in the form of a wiped off film. Such arrangements generally have a single evaporator body wherein there are individual working spaces provided with different vacuum pressures, adapted for degasing the treated liquid at a pressure of about 10.sup.-1 Torr, for preheating the liquid at a pressure of about 10.sup.-2 Torr and for molecular distilling it at a pressure of the order of 10.sup.-3 Torr. These individual working spaces are disposed within a single evaporator vessel and are separated from each other solely by rotating vacuum seals mounted between the evaporator vessel and the cooling cover so that the treated liquid passes from the working space with the lower vacuum to the working space with the higher vacuum and the rotating vacuum seals form together with the wipers in the individual working vacuum spaces a single unit.
In all of the now known arrangements for continuous vacuum and molecular distilling or evaporating liquid obtained in the form of a wiped off film, whether based on the principle of vertical cylindrical evaporator bodies (such as described, for example, in Czechoslovak Pat. Nos. 90,376 and 88,183, French Pat. No. 1,194,059, Czechoslovak Pat. Nos. 90,917, 114,756 and 114,714) or of evaporator bodies with vertical arrangement tapered in the direction of the trickling wiped off film (such as described, for example, in Czechoslovak Pat. No. 134,822) or of evaporator bodies having a combination of a cylinder and cone (such as described, for example, in Czechoslovak Pat. No. 134,822) or by using centrifuges (such as described, for example, in Czechoslovak Pat. Nos. 82,845 and 82,844, German published patent applications Nos. 1,080,972 and 1,014,971, French Pat. No. 1,025,087), the distilled liquid is gradually deprived of volatile materials in an individual evaporating stage, it is preheated in an equalizing vacuum stage and vacuum distilled in an individual high vacuum stage, whereby individual parts of the arrangement are, in case of a vertical arrangement connected, by means of double siphon seals (such as described, for example, in Czechoslovak Pat. No. 129,533) or in case of a horizontal arrangement by means of a system of vacuum dosing pumps. There is also known an arrangement for vacuum and molecular distilling liquid obtained from a wiped off film (such as described, for example, in Czechoslovak Pat. No. 154,171) wherein the agitation of the wiping off device in the individual working parts of the evaporator is effected by means of a single central shaft having a single vacuum seal in the part of the arrangement having the lowest vacuum. This arrangement is however provided with at least three individual wiping off systems, operating on three evaporator bodies. Therefore, the individual stages of the arrangement having a different vacuum are mutually connected by heated rotating siphon seals. A drawback of all of the described vacuum and molecular evaporators of the prior art resides in that they are composed of too many parts, and require a large number of vacuum sealed cooled flanges, a large number of auxiliary heating covers with individual temperature controls. It is therefore rather difficult to prevent mixing of the liquid passing through the device and the device generally gradually clogs due to decayed products which do not pass through. Such arrangements need individual wiping off systems in the individual parts with vacuum sealed mechanical transmission which require lubrication, so that the whole arrangement becomes rather complex and the assembling of it requires larger manipulation spaces. In the case of a vertical arrangement the siphon seals between the individual parts increase the overall height of the arrangement. In the case of a horizontal arrangement the pumps, which generally are gear wheel pumps, mounted between individual stages can be sources of frequent breakdowns, such as loss of vacuum, clogging, failure of operation due to mechanical dirt and similar malfunctioning.